This invention relates to an apparatus for recognizing a position of a pattern of an object and more particularly to an apparatus which can detect, with a high speed and a high optical S/N (signal to noise) ratio, the position and inclination of an IC chip pattern, and the electrode pad pattern provided on the IC chip, to achieving an efficient automatic wire bonding operation.
To manufacture a hybrid IC or the like, an IC chip pellet is mounted on a substrate, and a wire bonding is connected to the IC chip pellet by an automatic wire bonding apparatus.
To achieve successful automatic wire bonding in assembling semiconductor ICs or hybrid ICs, it is desired that the position of each bonding pad pattern of an IC chip be detected quickly and accurately. Unless the position of the pad pattern is detected quickly and accurately, the yield of products is reduced or the assembling process is delayed. The position of the wire bonding pad pattern is usually detected in the following manner.
First, an image pickup/sensing device such as a TV camera picks up/senses an image of a bonding pad pattern included in the IC chip pattern. Then, from the image of the bonding pad pattern on the IC chip there is obtained data indicating the position and the rotation of the IC pattern. Based on this data the position and inclination of the IC chip and the pads thereon are identified.
Two methods are known, which identify the chip pattern of an IC. One method is to detect a specific electrode pattern on an IC chip as recited in pages 168 to 174, No. 2 volume 19, Japanese Journal of Applied Physics (1980). The other is called multiple local pattern matching method as disclosed in pages 9, to 16, No. 1, volume 96-C, The Transactions of The Institute of Electrical Engineers of Japan (Jan. 1976).
In the first-mentioned method, the surface of an IC pellet is scanned by a single TV camera or the like. Image signals obtained by the scanning are converted into binary-coded signals, based on a desired slice level. Using the binary-coded signals, only the images of pads are displayed. Then, the positional relation or relative positions of a bonding pad existing on a single side of the chip and the other pads existing on the other two sides positioned at both terminals of the aforementioned single side of the chip is detected, thereby determing the position of the bonding pad based on the data of the entire chip.
In the multiple local pattern matching method, the surface of an IC pellet is scanned by a TV camera or the like. Image signals obtained by the scanning are converted into binary-coded signals having a desired slice level. The binary-coded signals representing electrode patterns are compared with the image data representing one of the electrode patterns which is predetermined and whose position is known. When some of the binary-coded signals are found to be identical with said image data, the position of the predetermined electrode pattern is identified and thus the position of a bonding pad is determined with respect to the position of the predetermined electrode pattern.
Both methods need to process image signals obtained by scanning the entire surface of an IC pellet. The amount of data that must be processed is so large that it inevitably takes a long time to identify the chip pattern. Further, the first-mentioned method cannot work if bonding pads are not arranged in orderly rows and columns. The second mentioned method may fail to identify the predetermined electrode pattern correctly, because in most cases some of the electrode patterns on an IC pellet are very similar to the predetermined one and are likely to be matched incorrectly.
Generally speaking, in a conventional method of identifying the pad pattern of an IC chip, the entire IC chip is within the view field, image signals are generated and converted into binary-coded signals having a single desired slice level, and the position of the pad pattern is detected directly from the binary-coded signals. This method, however, is disadvantageous because an enormous amount of data must be processed, and it takes a long time to identify the pad pattern. Further, with this method it is difficult to identify a desired pad pattern when the pad patterns are not arranged orderly, or when wire patterns having a width similar to that of the pad patterns are arranged near the pad patterns.
Further, in the prior art device, the optical signal-to-noise (S/N) ratio is inevitably low. That is, the resolution of the bonding pad pattern image is relatively low. Therefore, this method fails to detect the correct position of the bonding pad pattern when the IC chip is located too far from the image pickup device. Moreover, a wrong position of the bonding pad pattern may be detected if the bonding pads have scratches resulting from a previous electrical test.